Orthogonal frequency division multiplexing (OFDM) is a form of multiplexing that distributes data over a number of carriers that have a very precise spacing in the frequency domain. The precise spacing of the carriers provides several benefits such a high spectral efficiency, resiliency to radio frequency interference and lower multi-path distortion. Due to its beneficial properties and superior performance in multi-path fading wireless channels, OFDM has been identified as a useful technique in the area of high data-rate wireless communication, for example wireless metropolitan area networks (MAN). Wireless MAN are networks to be implemented over an air interface for fixed, portable, and mobile broadband access systems. Orthogonal frequency division multiple access (OFDMA) is a multiple access technology that utilizes OFDM techniques.
MIMO antenna systems axe also being considered for incorporation into Wireless MANs. MIMO systems use multiple transmitting and multiple receiving antennas for communication of information. MIMO antenna systems allow spatial diversity. Spatial diversity that takes advantage of transmitting data from multiple sources that have a known physical spacing.
Combining both OFDM and MIMO techniques provides a powerful technology for wireless broadband communication having advantages of both spatial diversity and frequency multiplexing. These attributes are especially useful in Non Line-of-Sight (NLOS) transmission scenarios that are encompassed by wireless MAN.
Responsibilities of the MAC layer of a network can involve forming a MAC protocol data unit (PDU) and scheduling multiple terminals within the network. Signaling in the MAC layer are used to tell the terminals when and/or where to look for information in a signal transmitted over the air interface.
Currently there are methodologies for dealing with particular aspects of wireless MAN, for example OFDMA communications. However, these methodologies do not deal with ways to incorporate the newer concepts of MIMO.